Chinese Patent Publication 1389604A to Wang et al. discloses a fiber known as polysulfonamide fiber (PSA) made by spinning a copolymer solution formed from a mixture of 50 to 95 weight percent 4,4′diaminodiphenyl sulfone and 5 to 50 weight percent 3,3′diaminodiphenyl sulfone copolymerized with equimolar amounts of terephthaloyl chloride in dimethylacetamide.
Chinese Patent Publication 1631941A to Chen et al. also discloses a method of preparing a PSA copolymer spinning solution formed from a mixture of 4,4′diaminodiphenyl sulfone and 3,3′diaminodiphenyl sulfone in a mass ratio of from 10:90 to 90:10 copolymerized with equimolar amounts of terephthaloyl chloride in dimethylacetamide.
In both these preparations, the copolymer chain has a high degree of para-orientation for high temperature structural stability. Unfortunately such systems tend to be insoluble in normal organic solvents, and therefore it is believed the addition of the meta-oriented 3,3′diaminodiphenyl sulfone provides enough disorder in this para-oriented system to allow the copolymer to be soluble in dimethylacetamide. Unfortunately, 3,3′diaminodiphenyl sulfone is expensive and is not widely available and therefore is undesirable as a copolymerizing species.
U.S. Pat. No. 4,169,932 to Sokolov et al. discloses preparation of poly(paraphenylene) terephthalamide (PPD-T) copolymers using tertiary amines to increase the rate of polycondensation. This patent discloses the PPD-T copolymer may be formed with terephthalic acid dichloride or a mixture of terephthalic acid dichloride (50-95 mole percent) and an aromatic acid dichloride of the diphenyl series (50-5 mole percent). This patent also discloses the PPD-T copolymer can be made by replacing 5 to 50 mole percent of the paraphenylene diamine (PPD) by another aromatic diamine such as 4,4′diaminodiphenyl sulfone, and provides an example of such a copolymer containing 95 mole percent paraphenylene diamine and 5 mole percent 4,4′diaminodiphenyl sulfone. While fibers made from the copolymers of Sokolov et al. are para-oriented, one of the benefits of PSA fiber is the high quantity of sulfone groups in the polymer chain that make the fiber exceptionally dyeable, something that would not be possible with the high PPD-content polymers of Sokolov.
Therefore, what is needed is a copolymer that is both soluble in normal organic solvents, has a high degree of para-oriented diamines for high temperature stability, and also has a high quantity of sulfone groups in the polymer chain.